Hey guys new here but not new to the car I've got a 03 G35 sedan recently purchased some 370Z Wheels 18x8 in the front 18x10 in the back my back ones rub when you hit a decent bump or turn to one side or the other is there a way to stiffen it up so I can keep them or am I better off just finding a more narrow or wheel thanks in advance guys

 

Pics would help, but you might be able to clear if you roll the lip on the rear fenders. I think it'll be tough (and not really worth it) to try and find stiffer springs with the same ride height.

 

Post which rear springs you have, there are colored dots on the spring and you can clean the spring with brakleen so you can see them again, usually you have to look up through the holes in the bottom of the spring bucket to see the color of the bottom dot. This will help determine exactly what springs you have and exactly which OEM springs could be used to stiffen the rear without affecting ride height.